Inspired by the way dolphins hunt, scientists have developed a new type of radar that can detect hidden surveillance equipment and explosives.

The twin inverted pulse radar (TWIPR) is able to distinguish true “targets” such as electronic circuits that can be used in explosive or espionage devices, from “clutter” (other metallic items like pipes, drink cans, or nails for example) that may be mistaken for a genuine target by traditional radar and metal detectors.

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The new system is based on a sonar concept called twin inverted pulse sonar (TWIPS), developed by Tim Leighton, professor from the University of Southampton’s Institute of Sound and Vibration research.

TWIPS exploits the natural abilities of dolphins to process their sonar signals to distinguish between targets and clutter in bubbly water.

Some dolphins blow “bubble nets” around schools of fish, which force the fish to cluster together. The dolphins’ sonar wouldn’t work if they couldn’t distinguish the fish from the bubbles.

The technique uses a signal consisting of two pulses in quick succession, one identical to the other, but phase inverted.

For the new study, published in Proceedings of the Royal Society A,the researchers showed that TWIPS could enhance linear scatter from the target, while simultaneously suppressing nonlinear scattering from oceanic bubbles.

Radar ‘knows’ targets and clutter

Leighton’s team proposed that the TWIPS method could be applied to electromagnetic waves and that the same technique would work with radar.

To test the proposal, they applied TWIPR radar pulses to a “target”—a dipole antenna with a diode across its feedpoint—to distinguish it from “clutter”—represented by an aluminium plate and a rusty bench clamp. The antenna is typical of circuitry in devices associated with covert communications, espionage, or explosives.

In the test, the tiny target showed up 100,000 times more powerfully than the clutter signal from an aluminum plate measuring 34 cm by 40 cm.

“As with TWIPS, the TWIPR method distinguishes linear scatterers from nonlinear ones. However, in scenarios for which TWIPS was designed, the clutter scatters nonlinearly and the target linearly—while in situations using TWIPR, these properties are reversed,” Leighton says.

Given that the diode target measures 6 cm in length, weighs 2.8 g, costs less than one Euro, and requires no batteries, it could allow the manufacture of small, lightweight and inexpensive location and identification tags for animals, infrastructure (pipelines, conduits for example) and for humans entering hazardous areas, particularly where they might be underground or buried.

The tags can easily be tuned to scatter-specific resonances to provide a unique identifier to a TWIPR pulse, something Leighton calls “the TWIPR fingerprint.”

Buried catastrophe victims not carrying such tags might still be located by TWIPR. It can carry the bandwidth to search for mobile phone resonances, to locate victims from their mobile phones, even when the phones are turned off or the batteries have no charge remaining.

“In addition to the applications discussed above, such technology could be extended to other radiations, such as magnetic resonance imaging (MRI) and light detection and ranging (LIDAR), which, for example, scatters nonlinearly from combustion products, offering the possibility of early fire detection systems.”